So there can't possibly exist a "workstation" without ECC RAM and a Xeon or Opteron? That seems a bit narrow. I think you're just drawing arbitrary lines here.
What about the PowerMac G5, was that that workstation? It had neither ECC nor a Xeon/Opteron.
I guess there weren't any Mac workstations prior to 2006!
Are you seeing how silly it is to draw distinctions yet?
I don't think silly. The definitions of all words change with usage. Some change radically. Many computer terms like "Workstation" change as technology changes. In the past usage was much more volatile because the communities were such a small subculture (Computer geeks of the 70's and 80's). I don't think it's silly to notice how the living English language works.
Currently a workstation is comprised of workstation grade components. Who decides which ones are, the manufacturers mostly. What are the main components of modern computer architecture?
CPU,
RAM,
GPU,
Storage,
PSU,
Case,
KB/M,
Where there are no workstation grade distinctions for a particular component like KB/M and case, we have to assume commonality between Workstation, Desktop, Server, and Enterprise-Server (AKA Heavy Metal) installations.
So to know if a computer station is a Desktop or Workstation the main topic in this thread, or even how much of a Workstation it is as it seems the lines overlap occasionally, all we need do is identify the components. The whole is equal to the sum of it's parts.
Is there a workstation classification among CPUs? Yes, commonly they are known: Xeon and Opteron. Currently speaking, without one of these it would be much more difficult to claim the system were a Workstation grade machine. The CPU type is currently (probably) the most important component in distinguishing classification.
Is there a workstation classification among types of Memory systems?
Yes, commonly it is known: Memory features like ECC define it. Currently speaking, without ECC it's more difficult to claim the system is a Workstation grade machine.
Is there a workstation classification among graphic subsystems (GPUs)? Yes, commonly they are known: FirePro and Quadro are two such. These both use ECC memory BTW.
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Currently speaking, without one of these it would be much more difficult to claim the system were a Workstation grade machine.
Is there such a classification for storage? I dunno for sure but I think not. There is enterprise class storage for both solid-state and traditional drives but lower spec drives seem to share a place in Desktop and Workstation machines. Some people think it's the other way round and Enterprise class drives share server and workstation space but desktop grade drives don't belong in a workstation. Due to the differing schools of thought on this it's hard to lend classification to a machine via it's storage subsystems.
PSU, Case, and KB/M are components where I at least see no distinction so if someone knows of such I'll leave it to them to bring it to light here. In the distant past in pre-286 tech days there were cases considered to be workstation grade in form-factor. These were known as full-tower cases. But soon after this changed as Sun Microsystems and SGI established systems which everyone agreed were the d'facto Workstations of the day - and many of them were in a "desktop" or "mid-tower" case.
I mentioned setting and tasking of a machine as well. A lot of this is carryover from past definitions of the term "Workstation" but also can be due to contemporary tasking. It's entirely proper for a person working in cubical workstation space or environment to refer to his or her computer as a workstation computer just as it would be for them to refer to their phone as their workstation phone. This would be especially true if the computer were the main work component of that workstation space. I think this usage needs to consider context more-so but again there is some definition overlap here where either definition lends weight to the other.